Although some rust spores have recently been found in Kentucky and Tennessee, this discovery does not necessarily mean that Asian soybean rust has moved north and is on the way to Illinois, according to Suzanne Bissonnette, the soybean rust educational state coordinator for University of Illinois Extension.
"The word 'rust' refers to a huge family of fungi that infect plants," Bissonnette says. "There are many hundreds of species of rust that infect green plants. It doesn't mean that just because they were sampling for soybean rust spores that those are the only rust spores that would be sucked up into a spore trap."
She notes that the fungi in the rust family have numerous microscopic features that look similar and thus they are organized into the rust family for purposes of identification by a mycologist or plant pathologist.
"If rust spores are found in a spore trap in a state, it only means that fungal spores that look like they are in the rust family are in the trap," Bissonnette says. "Many different kinds of rust spores could be in there."
Bissonnette points out the spores must be identified microscopically by an individual trained in rust taxonomy and properly identified as one of the species of soybean rust.
"Even then, that isn't the end of the identification process," she says. "There are two species of soybean rust, a severe one known as Asian soybean rust and a mild one that is of little or no concern. Laboratory tests, based on proteins on the outside of the rust spores, must be done to differentiate between the two known species of soybean rust."
She advises growers to await confirmation of the presence of Asian soybean rust before spraying the crop with a fungicide.
"It is important to make sure that the information you have is from a reliable source and that there is an indication that the rust species is actually Asian soybean rust and not just one of the innumerable other rust species we have floating around in the air at any given time," Bissonnette says. "You will save yourself time and money and will be a continuing good steward to the land by getting the right information before reacting."
The Web site www.soybeanrust.com includes updated information on fungicide guidelines, crop insurance and best farming practices, forecasts for dispersion of soybean rust spores, and the latest updates from the USDA Sentinel Plot Program.